1. Field of Invention
The present invention relates generally to ablation catheter systems that use electromagnetic energy in the microwave frequency range to ablate internal bodily tissues. More particularly, the present invention relates to methods of using a microwave ablation catheter which may be manipulated to form a loop within a cardiac chamber to facilitate the ablation of cardiac tissue.
2. Description of the Related Art
Catheter ablation is a therapy that is becoming more widely used for the treatment of medical problems such as cardiac arrhythmias, cardiac disrhythmias, and tachycardia. Most presently approved ablation catheter systems utilize radio frequency (RF) energy as the ablating energy source. However, RF energy has several limitations which include the rapid dissipation of energy in surface tissues. This rapid dissipation of energy often results in shallow "burns," as well as a failure to access deeper arrhythmic tissues. As such, catheters which utilize electromagnetic energy in the microwave frequency range as the ablation energy source are currently being developed. Microwave frequency energy has long been recognized as an effective energy source for heating biological tissues and has seen use in such hyperthermia applications as cancer treatment and the preheating of blood prior to infusions. Catheters which utilize microwave energy have been observed to be capable of generating substantially larger lesions than those generated by RF catheters, which greatly simplifies the actual ablation procedures. Some catheter systems which utilize microwave energy are described in the U.S. Pat. No. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346 to Grundy, et al.; and U.S. Pat. No. 5,314,466 to Stem, et al., each of which is incorporated herein by reference in its entirety.
Cardiac arrhythmias, which may be treated using catheter ablation, are generally circuits, known as "arrhythmia circuits," which form within the chambers of the heart. As is known to those skilled in the art, arrhythmia circuits are abnormal electrical connections which may form in various areas of the heart. For example, arrhythmia circuits may form around veins and/or arteries which lead away from and to the heart. Cardiac arrhythmias may occur in any area of the heart where arrhythmia circuits are formed.
Atrial fibrillation is one type of cardiac arrhythmia which may be treated using catheter ablation. For atrial fibrillation, which occurs in the left side of the heart, arrhythmia circuits form within the atria and between pulmonary veins. Due to the fact that these arrhythmia circuits often prevent the heart from beating normally, cutting the arrhythmia circuits is necessary to restore a normal heart beat. Many different cutting patterns may generally be implemented to cut arrhythmia circuits and, specifically, arrhythmia circuits formed within the left side of the heart. By way of example, a cutting pattern which involves the formation of a series of perpendicular, linear lesions may be used to cut circuits formed between pulmonary veins. When atrial fibrillation occurs in the right side of the heart, the cause of the atrial fibrillation is typically related to damage to cardiac tissue. In some cases, the atrial fibrillation may be attributed to scar tissue formed in the right side of the heart.
In order to properly position a conventional radio frequency catheter to form a desired cutting pattern, a catheter often must be repositioned for each ablation process, i.e., each time an overall linear lesion is to be formed. As will be appreciated by those skilled in the art, the tip of a catheter must often be repositioned in order to form a linear lesion. As the tip may only ablate a relatively small portion of tissue at a time, the tip must generally be moved, e.g., incrementally or point to point, in order for an overall linear lesion to be formed. That is, the process of placing an ablating tip in a desired position, then performing ablation, is typically repeated in order to form an overall lesion. In the event that ablation is occurring through a substantial amount of blood, coagulum may form on the tip. When too much coagulum forms, it may be necessary to remove the catheter from the body of the patient for cleaning, thereby requiring a reinsertion of the catheter to continue an overall ablation procedure. Reinserting the catheter into the body of a patient is often painful and time-consuming, especially if reinsertion occurs often.
While some microwave antenna catheters, as for example those with a steerable shaft, may effectively be positioned at any position within a heart, the antenna portion of the catheter may not be aligned in a desired direction. In other words, substantially any portion of the heart may be reached for ablation, although the antenna portion may not be oriented in a position or direction that enables a single linear lesion to be formed such that the desired tissue is ablated at one time.
Therefore, what is desired is a catheter with an antenna portion that may be readily conformed to and placed against the wall of a cardiac chamber such that a linear lesion may be formed. Specifically, what is desired is a manipulatable catheter with an antenna portion which may be readily positioned in substantially any orientation, e.g., an antenna portion that makes a line at any angle relative to a chosen planed in the heart, as well as a method for using such a catheter.